1. Field of the Invention
The invention relates to curable organic-inorganic hybrid compositions having a low optical loss, methods of making and using such compositions, and polymeric materials and articles made from such compositions. The compositions of the present invention are useful in the field of fiber optic communications.
2. Description of the Related Art
Very highly fluorinated polymeric materials have a low optical loss in the infrared, due to their low concentration of carbon-hydrogen, nitrogen-hydrogen, and oxygen-hydrogen bonds, all of which have a vibrational overtone absorption band around 1550 nm in wavelength. The common advantages of these materials are low optical loss, such as around 0.1-0.4 dB/cm at 1550 nm, and good thermal stability. While the highly fluorinated compositions can have a lower optical loss than the corresponding hydrogenated materials, they may also have a very low surface tension, poor compatibility with other materials, poor processability, poor wetting, and high shrinkage upon curing. Additionally, high fluorination also causes a significant depression in the refractive index of polymeric materials to a level down to below n=1.42 at 1550 nm.
Many efforts have been made to develop low optical loss organic-inorganic hybrid materials through the use of the sol-gel process. Although these hybrid materials are theoretically advantageous because of the optical clarity and hardness of the inorganic portion, the sol-gel process can result in materials with a high hydroxyl content. The hydroxide functional group has a strong vibrational overtone at around 1550 nm. Thus, in order to be useful in optical communications, sol-gel derived materials must be substantially dehydroxylated. However, the process of conventional dehydroxylation, requires a high temperature treatment and can damage the organic portion of the material, and can create cracking problems in films thicker than five microns and in monolithic materials. This cracking is due to high capillary pressure and the stress induced by shrinkage from the removal of water and alcohol through condensation reactions and evaporation. Further, the shrinkage of these materials makes them unsuitable for use in polymer microreplication processes. Another method for the incorporation of inorganics into processable polymer materials is the dispersion of silica or titantia particles prepared by the sol-gel process in fluorinated polyimide (ULTRADEL(copyright) 9020D) or polytetrafluoroethylene-derived (TEFLON(copyright)) organic polymers. One disadvantage of this method is the aggregation and/or agglomeration of particles due to the hydrophilicity of the surfaces of the particles.
One aspect of the present invention relates to an energy curable composition including condensed silica nanoparticles; an at least partially halogenated organosilane coupling agent; a halogenated energy curable monomer or oligomer; and an organosilane coupling agent containing an energy curable organic moiety.
Another aspect of the present invention relates to an energy curable composition including condensed silica nanoparticles; at least one coupling agent of the formula RfxRySiQ4xe2x88x92xxe2x88x92y wherein Rf is an at least partially fluorinated organic moiety bound to the silicon atom by a carbon atom, R is an organic moiety bound to the silicon atom by a carbon atom, Q is a hydrolyzable ligand selected from the group consisting of chlorine, bromine, iodine, a C1 to about C10 alkoxy, and a C1 to about C10 acyloxy, x is 1, 2, or 3, y is 0, 1, or 2, and the sum of x and y is no greater than 3; at least one coupling agent of the formula RdxRySiQ4xe2x88x92xxe2x88x92y wherein Rd is an organic moiety having an energy curable functional group bound to the silicon atom by a carbon atom, R is an organic moiety bound to the silicon atom by a carbon atom, Q is a hydrolyzable ligand selected from the group consisting of chlorine, bromine, iodine, a C1 to about C10 alkoxy, and a C1 to about C10 acyloxy, x is 1, 2, or 3, y is 0, 1, or 2, and the sum of x and y is no greater than 3; and at least one halogenated energy curable monomer or oligomer.
Another aspect of the present invention relates to a polymeric material including condensed silica nanoparticles having a mixture of organosilane coupling agents covalently bound to the exterior surface of the nanoparticies and a halogenated solid polymer matrix, wherein the mixture of organosilane coupling agents includes an at least partially fluorinated coupling agent and a coupling agent covalently bound to the polymer matrix, and the condensed silica nanoparticles are homogeneously dispersed in the solid polymer matrix.
Another aspect of the present invention relates to a planar optical device having a waveguide core and a waveguide cladding, wherein at least one of the waveguide core and waveguide cladding are made from the polymeric material of the present invention.
Another aspect of the present invention relates to a thin film optical device having alternating layers of transparent materials with differing refractive indices, wherein at least one of the materials is the polymeric material of the present invention.
Another aspect of the present invention relates to a monolithic optical element including the polymeric material of the present invention
Another aspect of the present invention relates to a process for making an energy curable composition by reacting condensed silica nanoparticles with a mixture of an at least partially fluorinated organosilane coupling agent and an organosilane coupling agent containing an energy curable organic moiety to yield nanoparticles with the mixture of the coupling agents covalently bound to the surface of the nanoparticles; and dispersing the nanoparticles so formed in at least one halogenated energy curable monomer or oligomer.
Another aspect of the present invention relates to a process for making a polymeric material by reacting condensed silica nanoparticles with a mixture of an at least partially fluorinated organosilane coupling agent and an organosilane coupling agent containing an energy curable organic moiety to yield nanoparticles with the mixture of the coupling agents covalently bound to the surface of the nanoparticles; dispersing the nanoparticles so formed in at least one halogenated energy curable monomer or oligomer; and curing the composition so formed with a source of energy.
Another aspect of the present invention is a process for making an article of manufacture comprising the steps of reacting condensed silica nanoparticles with an at least partially fluorinated organosilane coupling agent and an organosilane coupling agent containing an energy curable organic moiety to yield nanoparticles with the coupling agent or agents bound to the surface of the nanoparticles; dispersing the mixture so formed in at least one halogenated energy curable monomer or oligomer; contacting the composition so formed with a mold surface; curing the composition in contact with the mold with a source of energy; and removing the article so formed from the mold surface.
The materials of the present invention have a low optical loss in the infrared, less than 1.0 dB/cm at 1550 nm, making them suitable for use in devices for optical communication. Low shrinkage upon cure is observed, and low coefficient of thermal expansion, low thermo-optic coefficient and low birefringence of the polymeric material are expected due to the high inorganic content of these materials. The materials of the present invention may be formulated to have higher refractive indices than their wholly organic counterparts due to the higher refractive indices of the inorganic constituents. The energy curable composition has good wettability, and the polymeric material has good release characteristics from nickel microreplication tools as well as good adhesion to silaceous substrates such as glass, silica, and silicon, making the materials of this invention well suited for use in polymer microreplication processes.
Additional features and advantages of the invention will be set forth in the detailed description which follows, and in part will be readily apparent to those skilled in the art from the written description or recognized by practicing the invention as described in the written description and claims hereof, as well as the appended drawings.
It is to be understood that both the foregoing general description and the following detailed description are merely exemplary of the invention, and are intended to provide an overview or framework to understanding the nature and character of the invention as it is claimed:
The accompanying drawings are included to provide a further understanding of the invention, and are incorporated in and constitute a part of this specification. The drawings illustrate one or more embodiment(s) of the invention, and together with the description serve to explain the principles and operation of the invention.